Carrier transport and microstructure in semi-insulating polycrystalline silicon

Conductance in semi-insulating polycrystalline silicon (SIPOS) has been measured as a function of temperature and of applied transverse electric fields in materials whose oxygen content was varied from 2 up to 35 at.% O. Transmission electron microscopy reveals the presence of crystalline Si grains whose average radius decreases with the oxygen content, going up to ≈2 nm at the maximum oxygen concentration. The conduction is described by thermionic emission of electrons above intergrain barriers, tunneling through the barriers and Frenkel emission of electrons from the grain boundaries. The carrier transport parameters have been correlated to the material microstructure. At low oxygen contents, SIPOS has a `mozaic´ structure in which the grains are covered discontinuously by oxide. At 30 at.% O and above the material has a `shell´ microstructure, characterized by grains covered continuously by oxide shells. Upon annealing at 1200°C, at these large oxygen contents the authors observed a transition to a mosaic structure